Release: 1.4.0b1 beta release | Release Date: November 2, 2020

SQLAlchemy 1.4 Documentation

Session API

Session and sessionmaker()

Object Name Description

ORMExecuteState

Represents a call to the Session.execute() method, as passed to the SessionEvents.do_orm_execute() event hook.

Session

Manages persistence operations for ORM-mapped objects.

sessionmaker

A configurable Session factory.

SessionTransaction

A Session-level transaction.

class sqlalchemy.orm.sessionmaker(bind=None, class_=<class 'sqlalchemy.orm.session.Session'>, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw)

A configurable Session factory.

The sessionmaker factory generates new Session objects when called, creating them given the configurational arguments established here.

e.g.:

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

# an Engine, which the Session will use for connection
# resources
engine = create_engine('postgresql://scott:tiger@localhost/')

Session = sessionmaker(engine)

with Session() as session:
    session.add(some_object)
    session.add(some_other_object)
    session.commit()

Context manager use is optional; otherwise, the returned Session object may be closed explicitly via the Session.close() method. Using a try:/finally: block is optional, however will ensure that the close takes place even if there are database errors:

session = Session()
try:
    session.add(some_object)
    session.add(some_other_object)
    session.commit()
finally:
    session.close()

sessionmaker acts as a factory for Session objects in the same way as an Engine acts as a factory for Connection objects. In this way it also includes a sessionmaker.begin() method, that provides a context manager which both begins and commits a transaction, as well as closes out the Session when complete, rolling back the transaction if any errors occur:

Session = sessionmaker(engine)

wih Session.begin() as session:
    session.add(some_object)
    session.add(some_other_object)
# commits transaction, closes session

New in version 1.4.

When calling upon sessionmaker to construct a Session, keyword arguments may also be passed to the method; these arguments will override that of the globally configured parameters. Below we use a sessionmaker bound to a certain Engine to produce a Session that is instead bound to a specific Connection procured from that engine:

Session = sessionmaker(engine)

# bind an individual session to a connection

with engine.connect() as connection:
    with Session(bind=connection) as session:
        # work with session

The class also includes a method sessionmaker.configure(), which can be used to specify additional keyword arguments to the factory, which will take effect for subsequent Session objects generated. This is usually used to associate one or more Engine objects with an existing sessionmaker factory before it is first used:

# application starts, sessionmaker does not have
# an engine bound yet
Session = sessionmaker()

# ... later, when an engine URL is read from a configuration
# file or other events allow the engine to be created
engine = create_engine('sqlite:///foo.db')
Session.configure(bind=engine)

sess = Session()
# work with session

See also

Opening and Closing a Session - introductory text on creating sessions using sessionmaker.

Class signature

class sqlalchemy.orm.sessionmaker (sqlalchemy.orm.session._SessionClassMethods)

method sqlalchemy.orm.sessionmaker.__call__(**local_kw)

Produce a new Session object using the configuration established in this sessionmaker.

In Python, the __call__ method is invoked on an object when it is “called” in the same way as a function:

Session = sessionmaker()
session = Session()  # invokes sessionmaker.__call__()
method sqlalchemy.orm.sessionmaker.__init__(bind=None, class_=<class 'sqlalchemy.orm.session.Session'>, autoflush=True, autocommit=False, expire_on_commit=True, info=None, **kw)

Construct a new sessionmaker.

All arguments here except for class_ correspond to arguments accepted by Session directly. See the Session.__init__() docstring for more details on parameters.

Parameters
  • bind – a Engine or other Connectable with which newly created Session objects will be associated.

  • class_ – class to use in order to create new Session objects. Defaults to Session.

  • autoflush – The autoflush setting to use with newly created Session objects.

  • autocommit – The autocommit setting to use with newly created Session objects.

  • expire_on_commit=True – the Session.expire_on_commit setting to use with newly created Session objects.

  • info – optional dictionary of information that will be available via Session.info. Note this dictionary is updated, not replaced, when the info parameter is specified to the specific Session construction operation.

  • **kw – all other keyword arguments are passed to the constructor of newly created Session objects.

method sqlalchemy.orm.sessionmaker.begin()

Produce a context manager that both provides a new Session as well as a transaction that commits.

e.g.:

Session = sessionmaker(some_engine)

with Session.begin() as session:
    session.add(some_object)

# commits transaction, closes session

New in version 1.4.

method sqlalchemy.orm.sessionmaker.classmethod close_all()

inherited from the sqlalchemy.orm.session._SessionClassMethods.close_all method of sqlalchemy.orm.session._SessionClassMethods

Close all sessions in memory.

Deprecated since version 1.3: The Session.close_all() method is deprecated and will be removed in a future release. Please refer to close_all_sessions().

method sqlalchemy.orm.sessionmaker.configure(**new_kw)

(Re)configure the arguments for this sessionmaker.

e.g.:

Session = sessionmaker()

Session.configure(bind=create_engine('sqlite://'))
method sqlalchemy.orm.sessionmaker.classmethod identity_key(*args, **kwargs)

inherited from the sqlalchemy.orm.session._SessionClassMethods.identity_key method of sqlalchemy.orm.session._SessionClassMethods

Return an identity key.

This is an alias of identity_key().

method sqlalchemy.orm.sessionmaker.classmethod object_session(instance)

inherited from the sqlalchemy.orm.session._SessionClassMethods.object_session method of sqlalchemy.orm.session._SessionClassMethods

Return the Session to which an object belongs.

This is an alias of object_session().

class sqlalchemy.orm.ORMExecuteState(session, statement, parameters, execution_options, bind_arguments, compile_state_cls, events_todo)

Represents a call to the Session.execute() method, as passed to the SessionEvents.do_orm_execute() event hook.

New in version 1.4.

See also

Execute Events - top level documentation on how to use SessionEvents.do_orm_execute()

Class signature

class sqlalchemy.orm.ORMExecuteState (sqlalchemy.util.langhelpers.MemoizedSlots)

attribute sqlalchemy.orm.ORMExecuteState.session

The Session in use.

attribute sqlalchemy.orm.ORMExecuteState.statement

The SQL statement being invoked. For an ORM selection as would be retrieved from Query, this is an instance of select that was generated from the ORM query.

attribute sqlalchemy.orm.ORMExecuteState.parameters

Dictionary of parameters that was passed to Session.execute().

attribute sqlalchemy.orm.ORMExecuteState.bind_arguments

The dictionary passed as the Session.execute.bind_arguments dictionary. This dictionary may be used by extensions to Session to pass arguments that will assist in determining amongst a set of database connections which one should be used to invoke this statement.

attribute sqlalchemy.orm.ORMExecuteState.local_execution_options

Dictionary view of the execution options passed to the Session.execute() method. This does not include options that may be associated with the statement being invoked.

attribute sqlalchemy.orm.ORMExecuteState.execution_options
The complete dictionary of current execution options.

This is a merge of the statement level options with the locally passed execution options.

method sqlalchemy.orm.ORMExecuteState.invoke_statement(statement=None, params=None, execution_options=None, bind_arguments=None)

Execute the statement represented by this ORMExecuteState, without re-invoking events that have already proceeded.

This method essentially performs a re-entrant execution of the current statement for which the SessionEvents.do_orm_execute() event is being currently invoked. The use case for this is for event handlers that want to override how the ultimate Result object is returned, such as for schemes that retrieve results from an offline cache or which concatenate results from multiple executions.

When the Result object is returned by the actual handler function within SessionEvents.do_orm_execute() and is propagated to the calling Session.execute() method, the remainder of the Session.execute() method is preempted and the Result object is returned to the caller of Session.execute() immediately.

Parameters
Returns

a Result object with ORM-level results.

See also

Re-Executing Statements - background and examples on the appropriate usage of ORMExecuteState.invoke_statement().

attribute sqlalchemy.orm.ORMExecuteState.is_delete

return True if this is a DELETE operation.

attribute sqlalchemy.orm.ORMExecuteState.is_insert

return True if this is an INSERT operation.

attribute sqlalchemy.orm.ORMExecuteState.is_orm_statement

return True if the operation is an ORM statement.

This indicates that the select(), update(), or delete() being invoked contains ORM entities as subjects. For a statement that does not have ORM entities and instead refers only to Table metadata, it is invoked as a Core SQL statement and no ORM-level automation takes place.

attribute sqlalchemy.orm.ORMExecuteState.is_relationship_load

Return True if this load is loading objects on behalf of a relationship.

This means, the loader in effect is either a LazyLoader, SelectInLoader, SubqueryLoader, or similar, and the entire SELECT statement being emitted is on behalf of a relationship load.

attribute sqlalchemy.orm.ORMExecuteState.is_select

return True if this is a SELECT operation.

attribute sqlalchemy.orm.ORMExecuteState.is_update

return True if this is an UPDATE operation.

attribute sqlalchemy.orm.ORMExecuteState.lazy_loaded_from

An InstanceState that is using this statement execution for a lazy load operation.

The primary rationale for this attribute is to support the horizontal sharding extension, where it is available within specific query execution time hooks created by this extension. To that end, the attribute is only intended to be meaningful at query execution time, and importantly not any time prior to that, including query compilation time.

attribute sqlalchemy.orm.ORMExecuteState.load_options

Return the load_options that will be used for this execution.

attribute sqlalchemy.orm.ORMExecuteState.loader_strategy_path

Return the PathRegistry for the current load path.

This object represents the “path” in a query along relationships when a particular object or collection is being loaded.

attribute sqlalchemy.orm.ORMExecuteState.update_delete_options

Return the update_delete_options that will be used for this execution.

attribute sqlalchemy.orm.ORMExecuteState.user_defined_options

The sequence of UserDefinedOptions that have been associated with the statement being invoked.

class sqlalchemy.orm.Session(bind=None, autoflush=True, future=False, expire_on_commit=True, autocommit=False, twophase=False, binds=None, enable_baked_queries=True, info=None, query_cls=None)

Manages persistence operations for ORM-mapped objects.

The Session’s usage paradigm is described at Using the Session.

Class signature

class sqlalchemy.orm.Session (sqlalchemy.orm.session._SessionClassMethods)

method sqlalchemy.orm.Session.__init__(bind=None, autoflush=True, future=False, expire_on_commit=True, autocommit=False, twophase=False, binds=None, enable_baked_queries=True, info=None, query_cls=None)

Construct a new Session.

See also the sessionmaker function which is used to generate a Session-producing callable with a given set of arguments.

Parameters
  • autocommit

    Defaults to False. When True, the Session does not automatically begin transactions for individual statement exections, will acquire connections from the engine on an as-needed basis, releasing to the connection pool after each statement. Flushes will begin and commit (or possibly rollback) their own transaction if no transaction is present. When using this mode, the Session.begin() method may be used to explicitly start transactions, but the usual “autobegin” behavior is not present.

    Deprecated since version 1.4: The Session.autocommit parameter is deprecated and will be removed in SQLAlchemy version 2.0. The Session now features “autobegin” behavior such that the Session.begin() method may be called if a transaction has not yet been started yet. See the section Explicit Begin for background.

  • autoflush – When True, all query operations will issue a Session.flush() call to this Session before proceeding. This is a convenience feature so that Session.flush() need not be called repeatedly in order for database queries to retrieve results. It’s typical that autoflush is used in conjunction with autocommit=False. In this scenario, explicit calls to Session.flush() are rarely needed; you usually only need to call Session.commit() (which flushes) to finalize changes.

  • bind – An optional Engine or Connection to which this Session should be bound. When specified, all SQL operations performed by this session will execute via this connectable.

  • binds

    A dictionary which may specify any number of Engine or Connection objects as the source of connectivity for SQL operations on a per-entity basis. The keys of the dictionary consist of any series of mapped classes, arbitrary Python classes that are bases for mapped classes, Table objects and Mapper objects. The values of the dictionary are then instances of Engine or less commonly Connection objects. Operations which proceed relative to a particular mapped class will consult this dictionary for the closest matching entity in order to determine which Engine should be used for a particular SQL operation. The complete heuristics for resolution are described at Session.get_bind(). Usage looks like:

    Session = sessionmaker(binds={
        SomeMappedClass: create_engine('postgresql://engine1'),
        SomeDeclarativeBase: create_engine('postgresql://engine2'),
        some_mapper: create_engine('postgresql://engine3'),
        some_table: create_engine('postgresql://engine4'),
        })

  • class_ – Specify an alternate class other than sqlalchemy.orm.session.Session which should be used by the returned class. This is the only argument that is local to the sessionmaker function, and is not sent directly to the constructor for Session.

  • enable_baked_queries

    defaults to True. A flag consumed by the sqlalchemy.ext.baked extension to determine if “baked queries” should be cached, as is the normal operation of this extension. When set to False, all caching is disabled, including baked queries defined by the calling application as well as those used internally. Setting this flag to False can significantly reduce memory use, however will also degrade performance for those areas that make use of baked queries (such as relationship loaders). Additionally, baked query logic in the calling application or potentially within the ORM that may be malfunctioning due to cache key collisions or similar can be flagged by observing if this flag resolves the issue.

    New in version 1.2.

  • expire_on_commit

    Defaults to True. When True, all instances will be fully expired after each commit(), so that all attribute/object access subsequent to a completed transaction will load from the most recent database state.

    See also

    Committing

  • future

    if True, use 2.0 style transactional and engine behavior. Future mode includes the following behaviors:

    • The Session will not use “bound” metadata in order to locate an Engine; the engine or engines in use must be specified to the constructor of Session or otherwise be configured against the sessionmaker in use

    • The “subtransactions” feature of Session.begin() is removed in version 2.0 and is disabled when the future flag is set.

    • The behavior of the relationship.cascade_backrefs flag on a relationship() will always assume “False” behavior.

    New in version 1.4.

  • info – optional dictionary of arbitrary data to be associated with this Session. Is available via the Session.info attribute. Note the dictionary is copied at construction time so that modifications to the per- Session dictionary will be local to that Session.

  • query_cls – Class which should be used to create new Query objects, as returned by the Session.query() method. Defaults to Query.

  • twophase – When True, all transactions will be started as a “two phase” transaction, i.e. using the “two phase” semantics of the database in use along with an XID. During a commit(), after flush() has been issued for all attached databases, the TwoPhaseTransaction.prepare() method on each database’s TwoPhaseTransaction will be called. This allows each database to roll back the entire transaction, before each transaction is committed.

method sqlalchemy.orm.Session.add(instance, _warn=True)

Place an object in the Session.

Its state will be persisted to the database on the next flush operation.

Repeated calls to add() will be ignored. The opposite of add() is expunge().

method sqlalchemy.orm.Session.add_all(instances)

Add the given collection of instances to this Session.

method sqlalchemy.orm.Session.begin(subtransactions=False, nested=False, _subtrans=False)

Begin a transaction, or nested transaction, on this Session.

When used to begin the outermost transaction, an error is raised if this Session is already inside of a transaction.

Parameters
Returns

the SessionTransaction object. Note that SessionTransaction acts as a Python context manager, allowing Session.begin() to be used in a “with” block. See Explicit Begin for an example.

method sqlalchemy.orm.Session.begin_nested()

Begin a “nested” transaction on this Session, e.g. SAVEPOINT.

The target database(s) and associated drivers must support SQL SAVEPOINT for this method to function correctly.

For documentation on SAVEPOINT transactions, please see Using SAVEPOINT.

Returns

the SessionTransaction object. Note that SessionTransaction acts as a context manager, allowing Session.begin_nested() to be used in a “with” block. See Using SAVEPOINT for a usage example.

See also

Using SAVEPOINT

Serializable isolation / Savepoints / Transactional DDL - special workarounds required with the SQLite driver in order for SAVEPOINT to work correctly.

method sqlalchemy.orm.Session.bind_mapper(mapper, bind)

Associate a Mapper or arbitrary Python class with a “bind”, e.g. an Engine or Connection.

The given entity is added to a lookup used by the Session.get_bind() method.

Parameters
  • mapper – a Mapper object, or an instance of a mapped class, or any Python class that is the base of a set of mapped classes.

  • bind – an Engine or Connection object.

method sqlalchemy.orm.Session.bind_table(table, bind)

Associate a Table with a “bind”, e.g. an Engine or Connection.

The given Table is added to a lookup used by the Session.get_bind() method.

Parameters
  • table – a Table object, which is typically the target of an ORM mapping, or is present within a selectable that is mapped.

  • bind – an Engine or Connection object.

method sqlalchemy.orm.Session.bulk_insert_mappings(mapper, mappings, return_defaults=False, render_nulls=False)

Perform a bulk insert of the given list of mapping dictionaries.

The bulk insert feature allows plain Python dictionaries to be used as the source of simple INSERT operations which can be more easily grouped together into higher performing “executemany” operations. Using dictionaries, there is no “history” or session state management features in use, reducing latency when inserting large numbers of simple rows.

The values within the dictionaries as given are typically passed without modification into Core sqlalchemy.sql.expression.Insert() constructs, after organizing the values within them across the tables to which the given mapper is mapped.

New in version 1.0.0.

Warning

The bulk insert feature allows for a lower-latency INSERT of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw INSERT of records.

Please read the list of caveats at ORM Compatibility / Caveats before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters
  • mapper – a mapped class, or the actual Mapper object, representing the single kind of object represented within the mapping list.

  • mappings – a sequence of dictionaries, each one containing the state of the mapped row to be inserted, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary must contain all keys to be populated into all tables.

  • return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, Session.bulk_insert_mappings.return_defaults greatly reduces the performance gains of the method overall. If the rows to be inserted only refer to a single table, then there is no reason this flag should be set as the returned default information is not used.

  • render_nulls

    When True, a value of None will result in a NULL value being included in the INSERT statement, rather than the column being omitted from the INSERT. This allows all the rows being INSERTed to have the identical set of columns which allows the full set of rows to be batched to the DBAPI. Normally, each column-set that contains a different combination of NULL values than the previous row must omit a different series of columns from the rendered INSERT statement, which means it must be emitted as a separate statement. By passing this flag, the full set of rows are guaranteed to be batchable into one batch; the cost however is that server-side defaults which are invoked by an omitted column will be skipped, so care must be taken to ensure that these are not necessary.

    Warning

    When this flag is set, server side default SQL values will not be invoked for those columns that are inserted as NULL; the NULL value will be sent explicitly. Care must be taken to ensure that no server-side default functions need to be invoked for the operation as a whole.

    New in version 1.1.

method sqlalchemy.orm.Session.bulk_save_objects(objects, return_defaults=False, update_changed_only=True, preserve_order=True)

Perform a bulk save of the given list of objects.

The bulk save feature allows mapped objects to be used as the source of simple INSERT and UPDATE operations which can be more easily grouped together into higher performing “executemany” operations; the extraction of data from the objects is also performed using a lower-latency process that ignores whether or not attributes have actually been modified in the case of UPDATEs, and also ignores SQL expressions.

The objects as given are not added to the session and no additional state is established on them, unless the return_defaults flag is also set, in which case primary key attributes and server-side default values will be populated.

New in version 1.0.0.

Warning

The bulk save feature allows for a lower-latency INSERT/UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw INSERT/UPDATES of records.

Please read the list of caveats at ORM Compatibility / Caveats before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters
  • objects

    a sequence of mapped object instances. The mapped objects are persisted as is, and are not associated with the Session afterwards.

    For each object, whether the object is sent as an INSERT or an UPDATE is dependent on the same rules used by the Session in traditional operation; if the object has the InstanceState.key attribute set, then the object is assumed to be “detached” and will result in an UPDATE. Otherwise, an INSERT is used.

    In the case of an UPDATE, statements are grouped based on which attributes have changed, and are thus to be the subject of each SET clause. If update_changed_only is False, then all attributes present within each object are applied to the UPDATE statement, which may help in allowing the statements to be grouped together into a larger executemany(), and will also reduce the overhead of checking history on attributes.

  • return_defaults – when True, rows that are missing values which generate defaults, namely integer primary key defaults and sequences, will be inserted one at a time, so that the primary key value is available. In particular this will allow joined-inheritance and other multi-table mappings to insert correctly without the need to provide primary key values ahead of time; however, Session.bulk_save_objects.return_defaults greatly reduces the performance gains of the method overall.

  • update_changed_only – when True, UPDATE statements are rendered based on those attributes in each state that have logged changes. When False, all attributes present are rendered into the SET clause with the exception of primary key attributes.

  • preserve_order

    when True, the order of inserts and updates matches exactly the order in which the objects are given. When False, common types of objects are grouped into inserts and updates, to allow for more batching opportunities.

    New in version 1.3.

method sqlalchemy.orm.Session.bulk_update_mappings(mapper, mappings)

Perform a bulk update of the given list of mapping dictionaries.

The bulk update feature allows plain Python dictionaries to be used as the source of simple UPDATE operations which can be more easily grouped together into higher performing “executemany” operations. Using dictionaries, there is no “history” or session state management features in use, reducing latency when updating large numbers of simple rows.

New in version 1.0.0.

Warning

The bulk update feature allows for a lower-latency UPDATE of rows at the expense of most other unit-of-work features. Features such as object management, relationship handling, and SQL clause support are silently omitted in favor of raw UPDATES of records.

Please read the list of caveats at ORM Compatibility / Caveats before using this method, and fully test and confirm the functionality of all code developed using these systems.

Parameters
  • mapper – a mapped class, or the actual Mapper object, representing the single kind of object represented within the mapping list.

  • mappings – a sequence of dictionaries, each one containing the state of the mapped row to be updated, in terms of the attribute names on the mapped class. If the mapping refers to multiple tables, such as a joined-inheritance mapping, each dictionary may contain keys corresponding to all tables. All those keys which are present and are not part of the primary key are applied to the SET clause of the UPDATE statement; the primary key values, which are required, are applied to the WHERE clause.

method sqlalchemy.orm.Session.close()

Close this Session.

This clears all items and ends any transaction in progress.

If this session were created with autocommit=False, a new transaction will be begun when the Session is next asked to procure a database connection.

Changed in version 1.4: The Session.close() method does not immediately create a new SessionTransaction object; instead, the new SessionTransaction is created only if the Session is used again for a database operation.

method sqlalchemy.orm.Session.classmethod close_all()

inherited from the sqlalchemy.orm.session._SessionClassMethods.close_all method of sqlalchemy.orm.session._SessionClassMethods

Close all sessions in memory.

Deprecated since version 1.3: The Session.close_all() method is deprecated and will be removed in a future release. Please refer to close_all_sessions().

method sqlalchemy.orm.Session.commit()

Flush pending changes and commit the current transaction.

If no transaction is in progress, the method will first “autobegin” a new transaction and commit.

If 1.x-style use is in effect and there are currently SAVEPOINTs in progress via Session.begin_nested(), the operation will release the current SAVEPOINT but not commit the outermost database transaction.

If 2.0-style use is in effect via the Session.future flag, the outermost database transaction is committed unconditionally, automatically releasing any SAVEPOINTs in effect.

When using legacy “autocommit” mode, this method is only valid to call if a transaction is actually in progress, else an error is raised. Similarly, when using legacy “subtransactions”, the method will instead close out the current “subtransaction”, rather than the actual database transaction, if a transaction is in progress.

method sqlalchemy.orm.Session.connection(bind_arguments=None, close_with_result=False, execution_options=None, **kw)

Return a Connection object corresponding to this Session object’s transactional state.

If this Session is configured with autocommit=False, either the Connection corresponding to the current transaction is returned, or if no transaction is in progress, a new one is begun and the Connection returned (note that no transactional state is established with the DBAPI until the first SQL statement is emitted).

Alternatively, if this Session is configured with autocommit=True, an ad-hoc Connection is returned using Engine.connect() on the underlying Engine.

Ambiguity in multi-bind or unbound Session objects can be resolved through any of the optional keyword arguments. This ultimately makes usage of the get_bind() method for resolution.

Parameters
  • bind_arguments – dictionary of bind arguments. May include “mapper”, “bind”, “clause”, other custom arguments that are passed to Session.get_bind().

  • bind – deprecated; use bind_arguments

  • mapper – deprecated; use bind_arguments

  • clause – deprecated; use bind_arguments

  • close_with_result – Passed to Engine.connect(), indicating the Connection should be considered “single use”, automatically closing when the first result set is closed. This flag only has an effect if this Session is configured with autocommit=True and does not already have a transaction in progress.

  • execution_options

    a dictionary of execution options that will be passed to Connection.execution_options(), when the connection is first procured only. If the connection is already present within the Session, a warning is emitted and the arguments are ignored.

  • **kw – deprecated; use bind_arguments

method sqlalchemy.orm.Session.delete(instance)

Mark an instance as deleted.

The database delete operation occurs upon flush().

attribute sqlalchemy.orm.Session.deleted

The set of all instances marked as ‘deleted’ within this Session

attribute sqlalchemy.orm.Session.dirty

The set of all persistent instances considered dirty.

E.g.:

some_mapped_object in session.dirty

Instances are considered dirty when they were modified but not deleted.

Note that this ‘dirty’ calculation is ‘optimistic’; most attribute-setting or collection modification operations will mark an instance as ‘dirty’ and place it in this set, even if there is no net change to the attribute’s value. At flush time, the value of each attribute is compared to its previously saved value, and if there’s no net change, no SQL operation will occur (this is a more expensive operation so it’s only done at flush time).

To check if an instance has actionable net changes to its attributes, use the Session.is_modified() method.

method sqlalchemy.orm.Session.enable_relationship_loading(obj)

Associate an object with this Session for related object loading.

Warning

enable_relationship_loading() exists to serve special use cases and is not recommended for general use.

Accesses of attributes mapped with relationship() will attempt to load a value from the database using this Session as the source of connectivity. The values will be loaded based on foreign key and primary key values present on this object - if not present, then those relationships will be unavailable.

The object will be attached to this session, but will not participate in any persistence operations; its state for almost all purposes will remain either “transient” or “detached”, except for the case of relationship loading.

Also note that backrefs will often not work as expected. Altering a relationship-bound attribute on the target object may not fire off a backref event, if the effective value is what was already loaded from a foreign-key-holding value.

The Session.enable_relationship_loading() method is similar to the load_on_pending flag on relationship(). Unlike that flag, Session.enable_relationship_loading() allows an object to remain transient while still being able to load related items.

To make a transient object associated with a Session via Session.enable_relationship_loading() pending, add it to the Session using Session.add() normally. If the object instead represents an existing identity in the database, it should be merged using Session.merge().

Session.enable_relationship_loading() does not improve behavior when the ORM is used normally - object references should be constructed at the object level, not at the foreign key level, so that they are present in an ordinary way before flush() proceeds. This method is not intended for general use.

See also

relationship.load_on_pending - this flag allows per-relationship loading of many-to-ones on items that are pending.

make_transient_to_detached() - allows for an object to be added to a Session without SQL emitted, which then will unexpire attributes on access.

method sqlalchemy.orm.Session.execute(statement, params=None, execution_options={}, bind_arguments=None, _parent_execute_state=None, _add_event=None, **kw)

Execute a SQL expression construct.

Returns a Result object representing results of the statement execution.

E.g.:

from sqlalchemy import select
result = session.execute(
    select(User).where(User.id == 5)
)

The API contract of Session.execute() is similar to that of Connection.execute(), the 2.0 style version of Connection.

Changed in version 1.4: the Session.execute() method is now the primary point of ORM statement execution when using 2.0 style ORM usage.

Parameters
  • statement – An executable statement (i.e. an Executable expression such as select()).

  • params – Optional dictionary, or list of dictionaries, containing bound parameter values. If a single dictionary, single-row execution occurs; if a list of dictionaries, an “executemany” will be invoked. The keys in each dictionary must correspond to parameter names present in the statement.

  • execution_options – optional dictionary of execution options, which will be associated with the statement execution. This dictionary can provide a subset of the options that are accepted by Connection.execution_options(), and may also provide additional options understood only in an ORM context.

  • bind_arguments – dictionary of additional arguments to determine the bind. May include “mapper”, “bind”, or other custom arguments. Contents of this dictionary are passed to the Session.get_bind() method.

  • mapper – deprecated; use the bind_arguments dictionary

  • bind – deprecated; use the bind_arguments dictionary

  • **kw – deprecated; use the bind_arguments dictionary

Returns

a Result object.

method sqlalchemy.orm.Session.expire(instance, attribute_names=None)

Expire the attributes on an instance.

Marks the attributes of an instance as out of date. When an expired attribute is next accessed, a query will be issued to the Session object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

To expire all objects in the Session simultaneously, use Session.expire_all().

The Session object’s default behavior is to expire all state whenever the Session.rollback() or Session.commit() methods are called, so that new state can be loaded for the new transaction. For this reason, calling Session.expire() only makes sense for the specific case that a non-ORM SQL statement was emitted in the current transaction.

Parameters
  • instance – The instance to be refreshed.

  • attribute_names – optional list of string attribute names indicating a subset of attributes to be expired.

method sqlalchemy.orm.Session.expire_all()

Expires all persistent instances within this Session.

When any attributes on a persistent instance is next accessed, a query will be issued using the Session object’s current transactional context in order to load all expired attributes for the given instance. Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction.

To expire individual objects and individual attributes on those objects, use Session.expire().

The Session object’s default behavior is to expire all state whenever the Session.rollback() or Session.commit() methods are called, so that new state can be loaded for the new transaction. For this reason, calling Session.expire_all() should not be needed when autocommit is False, assuming the transaction is isolated.

method sqlalchemy.orm.Session.expunge(instance)

Remove the instance from this Session.

This will free all internal references to the instance. Cascading will be applied according to the expunge cascade rule.

method sqlalchemy.orm.Session.expunge_all()

Remove all object instances from this Session.

This is equivalent to calling expunge(obj) on all objects in this Session.

method sqlalchemy.orm.Session.flush(objects=None)

Flush all the object changes to the database.

Writes out all pending object creations, deletions and modifications to the database as INSERTs, DELETEs, UPDATEs, etc. Operations are automatically ordered by the Session’s unit of work dependency solver.

Database operations will be issued in the current transactional context and do not affect the state of the transaction, unless an error occurs, in which case the entire transaction is rolled back. You may flush() as often as you like within a transaction to move changes from Python to the database’s transaction buffer.

For autocommit Sessions with no active manual transaction, flush() will create a transaction on the fly that surrounds the entire set of operations into the flush.

Parameters

objects

Optional; restricts the flush operation to operate only on elements that are in the given collection.

This feature is for an extremely narrow set of use cases where particular objects may need to be operated upon before the full flush() occurs. It is not intended for general use.

method sqlalchemy.orm.Session.get(entity, ident, options=None, populate_existing=False, with_for_update=None, identity_token=None)

Return an instance based on the given primary key identifier, or None if not found.

E.g.:

my_user = session.get(User, 5)

some_object = session.get(VersionedFoo, (5, 10))

some_object = session.get(
    VersionedFoo,
    {"id": 5, "version_id": 10}
)

New in version 1.4: Added Session.get(), which is moved from the now deprecated Query.get() method.

Session.get() is special in that it provides direct access to the identity map of the Session. If the given primary key identifier is present in the local identity map, the object is returned directly from this collection and no SQL is emitted, unless the object has been marked fully expired. If not present, a SELECT is performed in order to locate the object.

Session.get() also will perform a check if the object is present in the identity map and marked as expired - a SELECT is emitted to refresh the object as well as to ensure that the row is still present. If not, ObjectDeletedError is raised.

Parameters
  • entity – a mapped class or Mapper indicating the type of entity to be loaded.

  • ident

    A scalar, tuple, or dictionary representing the primary key. For a composite (e.g. multiple column) primary key, a tuple or dictionary should be passed.

    For a single-column primary key, the scalar calling form is typically the most expedient. If the primary key of a row is the value “5”, the call looks like:

    my_object = session.get(SomeClass, 5)

    The tuple form contains primary key values typically in the order in which they correspond to the mapped Table object’s primary key columns, or if the Mapper.primary_key configuration parameter were used, in the order used for that parameter. For example, if the primary key of a row is represented by the integer digits “5, 10” the call would look like:

    my_object = session.get(SomeClass, (5, 10))

    The dictionary form should include as keys the mapped attribute names corresponding to each element of the primary key. If the mapped class has the attributes id, version_id as the attributes which store the object’s primary key value, the call would look like:

    my_object = session.get(SomeClass, {"id": 5, "version_id": 10})

  • options – optional sequence of loader options which will be applied to the query, if one is emitted.

  • populate_existing – causes the method to unconditionally emit a SQL query and refresh the object with the newly loaded data, regardless of whether or not the object is already present.

  • with_for_update – optional boolean True indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of Query.with_for_update(). Supersedes the Session.refresh.lockmode parameter.

Returns

The object instance, or None.

method sqlalchemy.orm.Session.get_bind(mapper=None, clause=None, bind=None, _sa_skip_events=None, _sa_skip_for_implicit_returning=False)

Return a “bind” to which this Session is bound.

The “bind” is usually an instance of Engine, except in the case where the Session has been explicitly bound directly to a Connection.

For a multiply-bound or unbound Session, the mapper or clause arguments are used to determine the appropriate bind to return.

Note that the “mapper” argument is usually present when Session.get_bind() is called via an ORM operation such as a Session.query(), each individual INSERT/UPDATE/DELETE operation within a Session.flush(), call, etc.

The order of resolution is:

  1. if mapper given and Session.binds is present, locate a bind based first on the mapper in use, then on the mapped class in use, then on any base classes that are present in the __mro__ of the mapped class, from more specific superclasses to more general.

  2. if clause given and Session.binds is present, locate a bind based on Table objects found in the given clause present in Session.binds.

  3. if Session.binds is present, return that.

  4. if clause given, attempt to return a bind linked to the MetaData ultimately associated with the clause.

  5. if mapper given, attempt to return a bind linked to the MetaData ultimately associated with the Table or other selectable to which the mapper is mapped.

  6. No bind can be found, UnboundExecutionError is raised.

Note that the Session.get_bind() method can be overridden on a user-defined subclass of Session to provide any kind of bind resolution scheme. See the example at Custom Vertical Partitioning.

Parameters
  • mapper – Optional mapper() mapped class or instance of Mapper. The bind can be derived from a Mapper first by consulting the “binds” map associated with this Session, and secondly by consulting the MetaData associated with the Table to which the Mapper is mapped for a bind.

  • clause – A ClauseElement (i.e. select(), text(), etc.). If the mapper argument is not present or could not produce a bind, the given expression construct will be searched for a bound element, typically a Table associated with bound MetaData.

method sqlalchemy.orm.Session.get_nested_transaction()

Return the current nested transaction in progress, if any.

New in version 1.4.

method sqlalchemy.orm.Session.get_transaction()

Return the current root transaction in progress, if any.

New in version 1.4.

method sqlalchemy.orm.Session.classmethod identity_key(*args, **kwargs)

inherited from the sqlalchemy.orm.session._SessionClassMethods.identity_key method of sqlalchemy.orm.session._SessionClassMethods

Return an identity key.

This is an alias of identity_key().

attribute sqlalchemy.orm.Session.identity_map = None

A mapping of object identities to objects themselves.

Iterating through Session.identity_map.values() provides access to the full set of persistent objects (i.e., those that have row identity) currently in the session.

See also

identity_key() - helper function to produce the keys used in this dictionary.

method sqlalchemy.orm.Session.in_nested_transaction()

Return True if this Session has begun a nested transaction, e.g. SAVEPOINT.

New in version 1.4.

method sqlalchemy.orm.Session.in_transaction()

Return True if this Session has begun a transaction.

New in version 1.4.

attribute sqlalchemy.orm.Session.info

A user-modifiable dictionary.

The initial value of this dictionary can be populated using the info argument to the Session constructor or sessionmaker constructor or factory methods. The dictionary here is always local to this Session and can be modified independently of all other Session objects.

method sqlalchemy.orm.Session.invalidate()

Close this Session, using connection invalidation.

This is a variant of Session.close() that will additionally ensure that the Connection.invalidate() method will be called on each Connection object that is currently in use for a transaction (typically there is only one connection unless the Session is used with multiple engines).

This can be called when the database is known to be in a state where the connections are no longer safe to be used.

Below illustrates a scenario when using gevent, which can produce Timeout exceptions that may mean the underlying connection should be discarded:

import gevent

try:
    sess = Session()
    sess.add(User())
    sess.commit()
except gevent.Timeout:
    sess.invalidate()
    raise
except:
    sess.rollback()
    raise

The method additionally does everything that Session.close() does, including that all ORM objects are expunged.

attribute sqlalchemy.orm.Session.is_active

True if this Session not in “partial rollback” state.

Changed in version 1.4: The Session no longer begins a new transaction immediately, so this attribute will be False when the Session is first instantiated.

“partial rollback” state typically indicates that the flush process of the Session has failed, and that the Session.rollback() method must be emitted in order to fully roll back the transaction.

If this Session is not in a transaction at all, the Session will autobegin when it is first used, so in this case Session.is_active will return True.

Otherwise, if this Session is within a transaction, and that transaction has not been rolled back internally, the Session.is_active will also return True.

method sqlalchemy.orm.Session.is_modified(instance, include_collections=True)

Return True if the given instance has locally modified attributes.

This method retrieves the history for each instrumented attribute on the instance and performs a comparison of the current value to its previously committed value, if any.

It is in effect a more expensive and accurate version of checking for the given instance in the Session.dirty collection; a full test for each attribute’s net “dirty” status is performed.

E.g.:

return session.is_modified(someobject)

A few caveats to this method apply:

  • Instances present in the Session.dirty collection may report False when tested with this method. This is because the object may have received change events via attribute mutation, thus placing it in Session.dirty, but ultimately the state is the same as that loaded from the database, resulting in no net change here.

  • Scalar attributes may not have recorded the previously set value when a new value was applied, if the attribute was not loaded, or was expired, at the time the new value was received - in these cases, the attribute is assumed to have a change, even if there is ultimately no net change against its database value. SQLAlchemy in most cases does not need the “old” value when a set event occurs, so it skips the expense of a SQL call if the old value isn’t present, based on the assumption that an UPDATE of the scalar value is usually needed, and in those few cases where it isn’t, is less expensive on average than issuing a defensive SELECT.

    The “old” value is fetched unconditionally upon set only if the attribute container has the active_history flag set to True. This flag is set typically for primary key attributes and scalar object references that are not a simple many-to-one. To set this flag for any arbitrary mapped column, use the active_history argument with column_property().

Parameters
  • instance – mapped instance to be tested for pending changes.

  • include_collections – Indicates if multivalued collections should be included in the operation. Setting this to False is a way to detect only local-column based properties (i.e. scalar columns or many-to-one foreign keys) that would result in an UPDATE for this instance upon flush.

method sqlalchemy.orm.Session.merge(instance, load=True)

Copy the state of a given instance into a corresponding instance within this Session.

Session.merge() examines the primary key attributes of the source instance, and attempts to reconcile it with an instance of the same primary key in the session. If not found locally, it attempts to load the object from the database based on primary key, and if none can be located, creates a new instance. The state of each attribute on the source instance is then copied to the target instance. The resulting target instance is then returned by the method; the original source instance is left unmodified, and un-associated with the Session if not already.

This operation cascades to associated instances if the association is mapped with cascade="merge".

See Merging for a detailed discussion of merging.

Changed in version 1.1: - Session.merge() will now reconcile pending objects with overlapping primary keys in the same way as persistent. See Session.merge resolves pending conflicts the same as persistent for discussion.

Parameters
  • instance – Instance to be merged.

  • load

    Boolean, when False, merge() switches into a “high performance” mode which causes it to forego emitting history events as well as all database access. This flag is used for cases such as transferring graphs of objects into a Session from a second level cache, or to transfer just-loaded objects into the Session owned by a worker thread or process without re-querying the database.

    The load=False use case adds the caveat that the given object has to be in a “clean” state, that is, has no pending changes to be flushed - even if the incoming object is detached from any Session. This is so that when the merge operation populates local attributes and cascades to related objects and collections, the values can be “stamped” onto the target object as is, without generating any history or attribute events, and without the need to reconcile the incoming data with any existing related objects or collections that might not be loaded. The resulting objects from load=False are always produced as “clean”, so it is only appropriate that the given objects should be “clean” as well, else this suggests a mis-use of the method.

See also

make_transient_to_detached() - provides for an alternative means of “merging” a single object into the Session

attribute sqlalchemy.orm.Session.new

The set of all instances marked as ‘new’ within this Session.

attribute sqlalchemy.orm.Session.no_autoflush

Return a context manager that disables autoflush.

e.g.:

with session.no_autoflush:

    some_object = SomeClass()
    session.add(some_object)
    # won't autoflush
    some_object.related_thing = session.query(SomeRelated).first()

Operations that proceed within the with: block will not be subject to flushes occurring upon query access. This is useful when initializing a series of objects which involve existing database queries, where the uncompleted object should not yet be flushed.

method sqlalchemy.orm.Session.classmethod object_session(instance)

inherited from the sqlalchemy.orm.session._SessionClassMethods.object_session method of sqlalchemy.orm.session._SessionClassMethods

Return the Session to which an object belongs.

This is an alias of object_session().

method sqlalchemy.orm.Session.prepare()

Prepare the current transaction in progress for two phase commit.

If no transaction is in progress, this method raises an InvalidRequestError.

Only root transactions of two phase sessions can be prepared. If the current transaction is not such, an InvalidRequestError is raised.

method sqlalchemy.orm.Session.query(*entities, **kwargs)

Return a new Query object corresponding to this Session.

method sqlalchemy.orm.Session.refresh(instance, attribute_names=None, with_for_update=None)

Expire and refresh the attributes on the given instance.

A query will be issued to the database and all attributes will be refreshed with their current database value.

Lazy-loaded relational attributes will remain lazily loaded, so that the instance-wide refresh operation will be followed immediately by the lazy load of that attribute.

Eagerly-loaded relational attributes will eagerly load within the single refresh operation.

Note that a highly isolated transaction will return the same values as were previously read in that same transaction, regardless of changes in database state outside of that transaction - usage of Session.refresh() usually only makes sense if non-ORM SQL statement were emitted in the ongoing transaction, or if autocommit mode is turned on.

Parameters
  • attribute_names – optional. An iterable collection of string attribute names indicating a subset of attributes to be refreshed.

  • with_for_update

    optional boolean True indicating FOR UPDATE should be used, or may be a dictionary containing flags to indicate a more specific set of FOR UPDATE flags for the SELECT; flags should match the parameters of Query.with_for_update(). Supersedes the Session.refresh.lockmode parameter.

    New in version 1.2.

method sqlalchemy.orm.Session.rollback()

Rollback the current transaction in progress.

If no transaction is in progress, this method is a pass-through.

In 1.x-style use, this method rolls back the topmost database transaction if no nested transactions are in effect, or to the current nested transaction if one is in effect.

When 2.0-style use is in effect via the Session.future flag, the method always rolls back the topmost database transaction, discarding any nested transactions that may be in progress.

method sqlalchemy.orm.Session.scalar(statement, params=None, execution_options={}, bind_arguments=None, **kw)

Execute a statement and return a scalar result.

Usage and parameters are the same as that of Session.execute(); the return result is a scalar Python value.

attribute sqlalchemy.orm.Session.transaction

The current active or inactive SessionTransaction.

Deprecated since version 1.4: The Session.transaction attribute is considered legacy as of the 1.x series of SQLAlchemy and will be removed in 2.0. For context manager use, use Session.begin(). To access the current root transaction, use Session.get_transaction(). (Background on SQLAlchemy 2.0 at: Migrating to SQLAlchemy 2.0)

May be None if no transaction has begun yet.

Changed in version 1.4: the Session.transaction attribute is now a read-only descriptor that also may return None if no transaction has begun yet.

class sqlalchemy.orm.SessionTransaction(session, parent=None, nested=False, autobegin=False)

A Session-level transaction.

SessionTransaction is produced from the Session.begin() and Session.begin_nested() methods. It’s largely an internal object that in modern use provides a context manager for session transactions.

Documentation on interacting with SessionTransaction is at: Managing Transactions.

Changed in version 1.4: The scoping and API methods to work with the SessionTransaction object directly have been simplified.

attribute sqlalchemy.orm.SessionTransaction.nested = False

Indicates if this is a nested, or SAVEPOINT, transaction.

When SessionTransaction.nested is True, it is expected that SessionTransaction.parent will be True as well.

attribute sqlalchemy.orm.SessionTransaction.parent

The parent SessionTransaction of this SessionTransaction.

If this attribute is None, indicates this SessionTransaction is at the top of the stack, and corresponds to a real “COMMIT”/”ROLLBACK” block. If non-None, then this is either a “subtransaction” or a “nested” / SAVEPOINT transaction. If the SessionTransaction.nested attribute is True, then this is a SAVEPOINT, and if False, indicates this a subtransaction.

New in version 1.0.16: - use ._parent for previous versions

Session Utilities

Object Name Description

close_all_sessions()

Close all sessions in memory.

make_transient(instance)

Alter the state of the given instance so that it is transient.

make_transient_to_detached(instance)

Make the given transient instance detached.

object_session(instance)

Return the Session to which the given instance belongs.

was_deleted(object_)

Return True if the given object was deleted within a session flush.

function sqlalchemy.orm.close_all_sessions()

Close all sessions in memory.

This function consults a global registry of all Session objects and calls Session.close() on them, which resets them to a clean state.

This function is not for general use but may be useful for test suites within the teardown scheme.

New in version 1.3.

function sqlalchemy.orm.make_transient(instance)

Alter the state of the given instance so that it is transient.

Note

make_transient() is a special-case function for advanced use cases only.

The given mapped instance is assumed to be in the persistent or detached state. The function will remove its association with any Session as well as its InstanceState.identity. The effect is that the object will behave as though it were newly constructed, except retaining any attribute / collection values that were loaded at the time of the call. The InstanceState.deleted flag is also reset if this object had been deleted as a result of using Session.delete().

Warning

make_transient() does not “unexpire” or otherwise eagerly load ORM-mapped attributes that are not currently loaded at the time the function is called. This includes attributes which:

  • were expired via Session.expire()

  • were expired as the natural effect of committing a session transaction, e.g. Session.commit()

  • are normally lazy loaded but are not currently loaded

  • are “deferred” via Deferred Column Loading and are not yet loaded

  • were not present in the query which loaded this object, such as that which is common in joined table inheritance and other scenarios.

After make_transient() is called, unloaded attributes such as those above will normally resolve to the value None when accessed, or an empty collection for a collection-oriented attribute. As the object is transient and un-associated with any database identity, it will no longer retrieve these values.

function sqlalchemy.orm.make_transient_to_detached(instance)

Make the given transient instance detached.

Note

make_transient_to_detached() is a special-case function for advanced use cases only.

All attribute history on the given instance will be reset as though the instance were freshly loaded from a query. Missing attributes will be marked as expired. The primary key attributes of the object, which are required, will be made into the “key” of the instance.

The object can then be added to a session, or merged possibly with the load=False flag, at which point it will look as if it were loaded that way, without emitting SQL.

This is a special use case function that differs from a normal call to Session.merge() in that a given persistent state can be manufactured without any SQL calls.

function sqlalchemy.orm.object_session(instance)

Return the Session to which the given instance belongs.

This is essentially the same as the InstanceState.session accessor. See that attribute for details.

function sqlalchemy.orm.util.was_deleted(object_)

Return True if the given object was deleted within a session flush.

This is regardless of whether or not the object is persistent or detached.

Attribute and State Management Utilities

These functions are provided by the SQLAlchemy attribute instrumentation API to provide a detailed interface for dealing with instances, attribute values, and history. Some of them are useful when constructing event listener functions, such as those described in ORM Events.

Object Name Description

del_attribute(instance, key)

Delete the value of an attribute, firing history events.

flag_dirty(instance)

Mark an instance as ‘dirty’ without any specific attribute mentioned.

flag_modified(instance, key)

Mark an attribute on an instance as ‘modified’.

get_attribute(instance, key)

Get the value of an attribute, firing any callables required.

get_history(obj, key[, passive])

Return a History record for the given object and attribute key.

History

A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.

init_collection(obj, key)

Initialize a collection attribute and return the collection adapter.

instance_state

Return the InstanceState for a given mapped object.

is_instrumented(instance, key)

Return True if the given attribute on the given instance is instrumented by the attributes package.

object_state(instance)

Given an object, return the InstanceState associated with the object.

set_attribute(instance, key, value[, initiator])

Set the value of an attribute, firing history events.

set_committed_value(instance, key, value)

Set the value of an attribute with no history events.

function sqlalchemy.orm.util.object_state(instance)

Given an object, return the InstanceState associated with the object.

Raises sqlalchemy.orm.exc.UnmappedInstanceError if no mapping is configured.

Equivalent functionality is available via the inspect() function as:

inspect(instance)

Using the inspection system will raise sqlalchemy.exc.NoInspectionAvailable if the instance is not part of a mapping.

function sqlalchemy.orm.attributes.del_attribute(instance, key)

Delete the value of an attribute, firing history events.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.

function sqlalchemy.orm.attributes.get_attribute(instance, key)

Get the value of an attribute, firing any callables required.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to make usage of attribute state as understood by SQLAlchemy.

function sqlalchemy.orm.attributes.get_history(obj, key, passive=symbol('PASSIVE_OFF'))

Return a History record for the given object and attribute key.

This is the pre-flush history for a given attribute, which is reset each time the Session flushes changes to the current database transaction.

Note

Prefer to use the AttributeState.history and AttributeState.load_history() accessors to retrieve the History for instance attributes.

Parameters
  • obj – an object whose class is instrumented by the attributes package.

  • key – string attribute name.

  • passive – indicates loading behavior for the attribute if the value is not already present. This is a bitflag attribute, which defaults to the symbol PASSIVE_OFF indicating all necessary SQL should be emitted.

See also

AttributeState.history

AttributeState.load_history() - retrieve history using loader callables if the value is not locally present.

function sqlalchemy.orm.attributes.init_collection(obj, key)

Initialize a collection attribute and return the collection adapter.

This function is used to provide direct access to collection internals for a previously unloaded attribute. e.g.:

collection_adapter = init_collection(someobject, 'elements')
for elem in values:
    collection_adapter.append_without_event(elem)

For an easier way to do the above, see set_committed_value().

Parameters
  • obj – a mapped object

  • key – string attribute name where the collection is located.

function sqlalchemy.orm.attributes.flag_modified(instance, key)

Mark an attribute on an instance as ‘modified’.

This sets the ‘modified’ flag on the instance and establishes an unconditional change event for the given attribute. The attribute must have a value present, else an InvalidRequestError is raised.

To mark an object “dirty” without referring to any specific attribute so that it is considered within a flush, use the flag_dirty() call.

See also

flag_dirty()

function sqlalchemy.orm.attributes.flag_dirty(instance)

Mark an instance as ‘dirty’ without any specific attribute mentioned.

This is a special operation that will allow the object to travel through the flush process for interception by events such as SessionEvents.before_flush(). Note that no SQL will be emitted in the flush process for an object that has no changes, even if marked dirty via this method. However, a SessionEvents.before_flush() handler will be able to see the object in the Session.dirty collection and may establish changes on it, which will then be included in the SQL emitted.

New in version 1.2.

See also

flag_modified()

function sqlalchemy.orm.attributes.instance_state()

Return the InstanceState for a given mapped object.

This function is the internal version of object_state(). The object_state() and/or the inspect() function is preferred here as they each emit an informative exception if the given object is not mapped.

function sqlalchemy.orm.instrumentation.is_instrumented(instance, key)

Return True if the given attribute on the given instance is instrumented by the attributes package.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required.

function sqlalchemy.orm.attributes.set_attribute(instance, key, value, initiator=None)

Set the value of an attribute, firing history events.

This function may be used regardless of instrumentation applied directly to the class, i.e. no descriptors are required. Custom attribute management schemes will need to make usage of this method to establish attribute state as understood by SQLAlchemy.

Parameters
  • instance – the object that will be modified

  • key – string name of the attribute

  • value – value to assign

  • initiator

    an instance of Event that would have been propagated from a previous event listener. This argument is used when the set_attribute() function is being used within an existing event listening function where an Event object is being supplied; the object may be used to track the origin of the chain of events.

    New in version 1.2.3.

function sqlalchemy.orm.attributes.set_committed_value(instance, key, value)

Set the value of an attribute with no history events.

Cancels any previous history present. The value should be a scalar value for scalar-holding attributes, or an iterable for any collection-holding attribute.

This is the same underlying method used when a lazy loader fires off and loads additional data from the database. In particular, this method can be used by application code which has loaded additional attributes or collections through separate queries, which can then be attached to an instance as though it were part of its original loaded state.

class sqlalchemy.orm.attributes.History(added, unchanged, deleted)

A 3-tuple of added, unchanged and deleted values, representing the changes which have occurred on an instrumented attribute.

The easiest way to get a History object for a particular attribute on an object is to use the inspect() function:

from sqlalchemy import inspect

hist = inspect(myobject).attrs.myattribute.history

Each tuple member is an iterable sequence:

  • added - the collection of items added to the attribute (the first tuple element).

  • unchanged - the collection of items that have not changed on the attribute (the second tuple element).

  • deleted - the collection of items that have been removed from the attribute (the third tuple element).

method sqlalchemy.orm.attributes.History.empty()

Return True if this History has no changes and no existing, unchanged state.

method sqlalchemy.orm.attributes.History.has_changes()

Return True if this History has changes.

method sqlalchemy.orm.attributes.History.non_added()

Return a collection of unchanged + deleted.

method sqlalchemy.orm.attributes.History.non_deleted()

Return a collection of added + unchanged.

method sqlalchemy.orm.attributes.History.sum()

Return a collection of added + unchanged + deleted.

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